The present invention relates to diesel lubricants, and more particularly to diesel lubricants containing additives which are effective to minimize undesirable viscosity increases of the lubricant when the lubricant is used in diesel engines. The invention also relates to methods of preparing basic alkali and alkaline earth metal sulfonates, and a method of operating diesel engines which comprises lubricating said engines during operation with the diesel lubricants of the invention.
It is well known that lubricating oils tend to deteriorate under conditions of use in present day internal combustion engines resulting in the formation of sludge, lacquer, carbonaceous materials and resinous materials which tend to adhere to the various engine parts, in particular, the engine rings, grooves and skirts.
Furthermore, diesel engines operated at low-speed and high-torque such as under prolonged idle and stop-and-go conditions have experienced extensive and undesirable thickening of the lubricant. It has been suggested in the prior art that the undesirable thickening of the oil is caused by the high levels of insolubles (soot).
One class of compounds which has been suggested for use in lubricating oils, particularly diesel oils, are the normal and overbased sulfurized calcium alkyl phenolates such as described in U.S. Pat. Nos. 3,474,035; 3,528,917; and 3,706,632. These materials function as detergents and dispersants, and also are reported to exhibit antioxidant and anti- thickening properties. Another multi-purpose additive for lubricating oils having antioxidant, anti-thickening, anti-corrosion and detergent properties is described in U.S. Pat. No. 3,897,352. The additive described in this patent comprises a sulfurized, Group II metal nitrated alkyl phenolate.
As will be described more fully hereinafter, the present invention relates to a diesel lubricant containing certain specified types of carboxylic derivative compositions as dispersants, certain basic alkali and alkaline earth metal salts, acting as detergents. This combination of specific dispersant, and detergent, is effective to minimize undesirable viscosity increases of diesel lubricants when used in diesel engines.
Lubricating oil formulations containing oil-soluble carboxylic acid derivatives, and in particular, those obtained by the reaction of a carboxylic acid with an amino compound have been described previously such as in U.S. Pat. Nos. 3,018,250; 3,024,195; 3,172,892; 3,216,936; 3,219,666; and 3,272,746. Many of the above-identified patents also describe the use of such carboxylic acid derivatives in lubricating oils in combination with ash containing detergents including basic metal salts of acidic organic materials such as sulfonic acids, carboxylic acids, etc.
The particular type of carboxylic acid derivative composition utilized in the diesel lubricant of the present invention are described generally in U.S. Pat. No. 4,234,435. This patent also describes lubricating compositions containing said carboxylic acid derivative compositions in combination with other additives such as fluidity modifiers, auxiliary detergents and dispersants of the ash producing or ashless type, oxidation inhibitors, etc. A lubricating composition containing the carboxylic acid derivative, a basic calcium sulfonate, and other traditional additives is described in the '435 patent in Col. 52, lines 1-8.
The second critical component of the diesel lubricants of the present invention is at least one basic alkali or alkaline earth metal salt of at least one acidic organic compound having a metal ratio of at least about 2. Such compositions generally are referred to in the art as metallic or ash-detergents, and the use of such detergents in the lubricating oil formulations has been suggested in many prior art patents. For example, Canadian Patent 1,055,700 describes the use of basic alkali sulfonate dispersions in crankcase lubricants for both spark-ignited and compression-ignited internal combustion engines. The Canadian patent suggests that the basic alkali sulfonate dispersions can be used alone or in combination with other lubricant additives known in the art such as ashless dispersants including esters or amides of hydrocarbon substituted succinic acids.
Even though detergents and dispersants, both of the ash and the ashless-type have been utilized previously in diesel lubricants, many of these lubricants have continued to exhibit undesirable thickening, especially under low-speed, high-torque operation unless relatively large amounts of the detergents and dispersants are incorporated into the diesel lubricants. The use of large amounts of detergents and dispersants generally is undesirable because of the added cost.
In order to constitute an acceptable heavy duty diesel lubricant, a lubricant must demonstrate passing performance in standard tests. Three such tests are the Caterpillar 1-G2, a single cylinder high temperature deposit evaluation, the CLR L-38, demonstrating copper/lead bearing protection and the Mack T-7. Acceptable performance in the first two tests is required for an API CD quality rating. However, neither of these two tests measures the lubricants ability to control viscosity increase. The Mack T-7 test is designed to guage this ability. As set forth more fully below, the Mack T-7 test is conducted with a large diesel engine run at low speed, high torque conditions. This test simulates the conditions which exist when a large diesel truck is just beginning to move and there is a heavy load on the engine. The test oil is placed in the engine, and the engine is run for 150 hours. The viscosity of the oil is monitored over time and the slope of the viscosity increase curve is calculated. A viscosity increase of 0.04 cSt/hour or less over the last 50 hours is considered to be a passing level. There continues to be a need in the industry for compositions which can be added to diesel lubricants which will minimize, if not prevent, undesirable viscosity increase of the lubricant when used in diesel engines, and when formulated into diesel lubricants, the lubricants are capable of achieving the CLR L-38, Caterpillar 1-G2, and Mack T-7 level performance without significantly adding to the cost of the diesel lubricant.